In a fire control mechanism, pulling a trigger breaks the engagement of a sear with a hammer, which is then pivoted by spring force into contact with a firing pin. The inertia of the moving hammer provides an impact force to the firing pin to detonate an ammunition primer.
In an effort to reduce the overall weight of a firearm, material may be removed from virtually any part, or parts may be made from lower density materials. If the mass of the hammer is reduced too much, it will lack sufficient momentum or inertia to strike the firing pin with enough force or may rebound from the firing pin causing “hammer bounce.” If, in an effort to overcome the lack of hammer mass by increasing its velocity, the spring force is increased, other problems may be created by the significantly increased amount of force required to cock the hammer.